This content is PDF only. Please click on the PDF icon to access.
Abstract
PURPOSE: Recent studies have indicated that certain aldose reductase inhibitors prevent the formation of cataracts in naphthalene-fed rats. The study was designed to investigate whether aldose reductase itself is involved in the metabolism of naphthalene in the lens and the mechanism of this cataract formation. METHODS: Aldose reductase was purified from whole rat lens using a series of chromatographic steps that include gel filtration, affinity chromatography, and chromatofocusing. The dehydrogenase activity of the purified enzyme was evaluated with 1,2-dihydro-1,2-dihydroxynaphthalene (naphthalene dihydrodiol) as substrate. The same dehydrogenase activity was also examined with the recombinant protein obtained from rat lens aldose reductase clone. RESULTS: Throughout the purification steps, dehydrogenase activity with naphthalene dihydrodiol as substrate coeluted with aldose reductase activity assayed with DL-glyceraldehyde as substrate. The purified aldose reductase, which appeared as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, displayed dehydrogenase activity with naphthalene dihydrodiol as a substrate similar to that observed with the crude extract from whole rat lens. Recombinant protein from rat lens aldose reductase clone also displayed dehydrogenase activity similar to that observed with purified rat lens aldose reductase. Both the reductase and dehydrogenase activities of purified aldose reductase were inhibited by aldose reductase inhibitors. However, inhibition of dehydrogenase activity was less than reductase activity. Aldehyde reductase, an another nicotinamide adenine dinucleotide phosphate-dependent reductase, also displayed dihydrodiol dehydrogenase activity with naphthalene dihydrodiol and this activity was also inhibited by aldose reductase inhibitors. CONCLUSIONS: Aldose reductase displays dehydrogenase activity in addition to reductase activity. In rat lens aldose reductase is a major protein associated with naphthalene dihydrodiol dehydrogenase activity. This suggests that aldose reductase is linked to 1,2-dihydroxynaphthalene formation in rat lens and the subsequent formation of cataracts in naphthalene-fed rats.